1. Field of the Invention
The present invention relates to recording and/or reproducing apparatus. More particularly, the present invention concerns means for controlling the relative movement between a recording and/or reproducing head means and a record bearing medium in a recording and/or reproducing apparatus.
2. Description of the Related Art
In a recording and/or reproducing apparatus such as, for example, a still video apparatus using a magnetic disc as a record bearing medium, a motor which rotates the disc relative a magnetic head is controlled so that the disc rotation is synchronized with a reference signal. Specifically, the disc rotation is controlled by a deviation signal which corresponds to the phase difference between a rotation phase signal and a reference signal.
The rotation signal usually has a cycle equal to that of the disc or the rotor rotation (i.e. once per one revolution); and the reference signal usually comprises a TV vertical synchronization signal.
However, in prior control arrangements a delay was experienced between the starting of the drive motor and the achievement of synchronization. Also, since the deviation signal could be obtained only once per one revolution of disc or the rotor, a poor response and low precision of synchronization was experienced.
In Japanese Patent Application No. Sho. 60-53144 53144/1985. (U.S. Counterpart: Patent Application Ser. No. 839.058; Filed: Mar. 13, 1986; Title: "Rotary body drive device"; Inventor: Nobuo Fukushima; Assigner; to same assignee as the present invention), there is disclosed a recording and/or reproducing apparatus which comprises a magnetic head, a motor, a motor control circuit and a synchronization signal generation circuit. The magnetic head magnetically records signals on and/or reproduces signals from a magnetic disc while the motor rotates the disc relative to the head. The motor control circuit includes reference signal generation means and phase control means. The reference signal generation means generates a reference signal for phase control when the rotation of the disc reaches a predetermined speed. The phase control means controls the rotation phase of the disc on the basis of the reference signal and a disc rotation speed signal known as an FG signal. Also the synchronization signal generation means generates, in response to a specific rotation phase of the disc, a synchronization signal to be used in a signal processing circuit.
The reference signal generation means may be arranged to generate the reference signal on the basis of the FG signal.
On the other hand, in a conventional motor control arrangement, a considerable time is needed from the start of the motor to share synchronization. This is due to fluctuations of the load on the motor caused by changes in environmental conditions such as temperature and humidity, etc. Even if the time to the phase synchronization is adjusted satisfactorily, when the power supply to the system is turned on after it has been turned off, considerable time is required to achieve phase synchronization again.
The control amount needed to control a motor so as to rotate the head and the medium relative to one another is generally given by the following formula (1): EQU Control amount=(G1).times.(PDA)+(G2).times.(SDA)+(G3).times.(IPDA)+(Offset value C) (1)
Here, PDA is the phase deviation amount, SDA is the speed deviation amount and IPDA is the "integrated value of the phase deviation amount. Also, G1, G2 and G3 are constants. The offset value C represents the control amount required to control the motor at a predetermined speed, for example, 3,600 r.p.m. when the phase deviation amount, the speed deviation amount and the integrated value of the phase deviation amount are all zero. The control amount shown by formula (1) may be supplied from a system controller in the recording and/or reproducing apparatus to control the speed and the phase of the motor.
The integrated value of the phase deviation amount in the third term of the formula (1) represents the low frequency component in the fluctuation of the load to the motor. In the formula (1), when the load increases due to change in the temperature or the humidity, etc., of the surroundings, the above mentioned integrated value increases, and conversely, when the load decreases, the integrated value decreases. On the other hand, the time constant necessary for the integration of the phase deviation amount is determined by the constant G3 and cannot be set at a very small value because of the stability of the control. Accordingly, a relatively long time is required from the start of the motor until the integration value is determined. During this time the speed and the phase of the motor are offset from their respective target values. Thus, as a result, the required time to phase synchronization becomes long. Also, even if the control amount is set at a desired amount, when the power supply to the system is turned on after it has been turned off, considerable time is needed to achieve the phase synchronization again.